Two things I would look at, the front band and the high gear clutches
I would see how far out the front band adjusters is out now then count the amount of full turns it takes to get it to have 72inch lbs. torque to snug it up against the front drum, if it takes 6 or more turns look closely at the front drum and band
If it takes less than 5 full turns to snug it to 72 inch Lbs. then take the tranny out and look at the front clutches
In the future I wouldn't run it anymore after the first flare on the gear change, either correct it at the track if it is the front drum or take it home and fix it if it isn't the front band